This invention relates to a circumferential flow type fuel pump, and more particularly to a circumferential flow type fuel pump comprising a circumferential flow type liquid pump unit used for a vehicle internal combustion engine.
A conventional circumferential flow type fuel pump for vehicles will be described with reference to FIGS. 1, 2 and 3. FIG. 1 is a sectional view showing the conventional circumferential flow type fuel pump, FIG. 2 is a sectional view taken along line II--II in FIG. 1, and FIG. 3 is a sectional view taken along line III--III in FIG. 2.
As shown in these figures, a pump body 1 comprises an electrical feeder section 2, a rotor 3, a circumferential flow type pump section 4, and an outer cylinder 5. The shaft 3a of the rotor 3 is rotatably supported by a first bearing 2a in the electrical feeder section 2 and a second bearing 4a in the pump section 4.
The pump section 4 is made up of a pump casing 41, an impeller 42, and a pump cover 43. The pump casing 41 is press-fitted in the outer cylinder 5. The pump cover 43 is fixedly secured to the open end of the outer cylinder 5 by caulking. The impeller 42 is interposed between the pump casing 41 and the pump cover 43. The impeller 42 is mounted on the shaft 3a of the rotor 3 so that it is rotated together with the latter 3.
First and second recesses 41a and 43a are formed in the pump casing 41 and the pump cover 43, respectively, in such a manner that they confronted each other. That is, a circumferential fuel flow passage 44 is formed along the peripheral portion of the impeller 42. A number of pumping blades 42a are provided on the peripheral portion of the impeller 42 which confronts with the fuel flow passage 44.
The upstream end of the fuel flow path 44 is communicated with a fuel sucking inlet 45 provided in the pump cover 43, while the downstream end is communicated through a fuel discharging outlet 46 provided in the pump casing 41 and a motor chamber 6 with a lead-out section 21 coupled to the electrical feeder section 2.
In the fuel flow passage 44, a portion having a predetermined length from the upstream end is formed into a flow passage enlarging part which increases the section of the flow passage radially inwardly. A small hole, namely, a gas discharging hole 47 is formed in the downstream end portion of the flow passage enlarging section so that the fuel flow passage 44 is communicated with the outside the pump body 1.
Now, the operation of the fuel pump thus constructed will be described.
An external power source applies current through the electrical feeder section 2 to the rotor 3 to rotate the latter. Accordingly, the impeller 41 mounted on the shaft of the rotor 3 is rotated to operate as a pump, so that fuel is sucked in through the fuel sucking inlet 45. The fuel thus sucked is supplied, for instance, to an engine (not shown) via the fuel flow passage 44, the discharging outlet 46, the motor chamber 6 and the lead-out section 21.
If, in this operation, the fuel in the fuel flow passage contains bubbles, the fuel viscosity is decreased, so that the friction between the fuel and the impeller is decreased. That is, the fuel pump is decreased in performance, since it relies on the friction between the impeller 42 and the fuel.
In order to overcome this difficulty, the gas discharging hole 47 is provided to remove the bubbles from the fuel. This will be described in more detail. The bubbles in the fuel are different in specific gravity and accordingly in the centrifugal force acting thereon from the fuel. Therefore, the bubbles are collected in the inner peripheral portion of the fuel flow passage 44, i.e., in the flow passage enlarging part 44a while flowing down. As a result, the bubbles are discharged through the gas discharging hole 47 provided in the downstream end portion of the flow passage enlarging part 44a.
It is true that, in the conventional circumferential flow type fuel pump for a vehicle, the bubbles in the fuel can be removed to a certain extent. However, the bubble removing capacity is not sufficient. That is, under severe operating conditions, such as at a high fuel temperature, it is impossible to completely remove the bubbles from the fuel, and accordingly, the pumping performance is greatly decreased.